By default, the Tectia client/server solution uses private and public keys stored in the IETF standard Secure Shell v2 format. However, Tectia Client and Server can also use keys and related files in the legacy OpenSSH format.

This link points you to Tectia documentation regarding this (check out chapter 4.5).

As well, this other link explains you the differences between OpenSSH style of keys and Tectia style of keys.